Niche and Neutrality Work Differently in Microbial Communities in Fluidic and Non-fluidic Ecosystems

This data-intensive study investigated the delicate balance of niche and neutrality underlying microbial communities in freshwater ecosystems through comprehensive application of high-throughput sequencing, species abundance distribution (SAD), and the neutral community model (NCM), combined with species diversity and phylogenetic measures, which unite the traditional and microbial ecology. On the genus level, 45.10% and 41.18% of the water samples could be explained by the log-normal and Volkov model respectively, among which 31.37% could fit both models. Meanwhile, 55.56% of the sediment samples could be depicted by the log-normal model, and Volkov-fitted samples comprised only 13.33%. Besides, operational taxonomic units (OTUs) from water samples fit Sloan's neutral model significantly better than those in sediment. Therefore, it was concluded that deterministic processes played a great role in both water and sediment ecosystems, whereas neutrality was much more involved in water assemblages than in non-fluidic sediment ecosystems. Secondly, log-normal fitted samples had lower phylogenetic species variability (PSV) than Volkov-fitted ones, indicating that niche-based communities were more phylogenetically clustered than neutrally assembled counterparts. Additionally, further testing showed that the relative richness of rare species was vital to SAD modeling, either niche-based or neutral, and communities containing fewer rare species were more easily captured by theoretical SAD models.